There are many merits in this proposal:
--farm lands are not lost
--water loss due to evaporation is nil
--the water stays pollution free
--with sunlight excluded, the water stays potable for years
--being shallow, it can be pumped out economically, manually
--the earth supporting the sphere all around strengthens the structure

The geometry of geo domes gets complex if one attempts finer and finer forms of a sphere. At the fundamental level however is a dodecahedron: it is a coarse faceted sphere made of 12 flat hexagonal panels. For water storage purposes these would do well. For the best introduction to dodecahedrons go to this page and from there click the link entitled ‘Domes’.

The beautiful drawings there will help you visualise how these tanks can be easily erected underground. First the top soil is scooped out and set aside. Then the land is excavated. Ready made hexagonal panels are used. The bottom half of the sphere is erected . Their joints are sealed with rich concrete. Then using steadies, the upper hemisphere is erected and sealed. The twelfth panel is finally lowered to close the sphere. This will carry a manhole, the inlet pipe etc. Soil is filled back and top soil is restored.

The hexagonal panels themselves will be designed to a nation wide standard and the process of making them soundly will be developed and released in the public domain. Local businesses will manufacture these adhering to quality norms, using local labour. Now, it is structurally sounder to make the hexagons as small shallow pieces rather than flat ones. These will be consequent of design studies. At any rate, they should be stackable for economic transport.

So we have local employment growth and water harvesting at low cost. These spheres buried in catchment areas will arrest rain water run off. We in fact have an alternative to even check dams. Widely dispersed water availability will motivate people to move into wastelands and begin appropriate crop cultivation. These spheres will also serve afforestation programs by providing water for early plantations.

Is there an enthusiast out there to commission a study of this idea by specialists?
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Click here for a useful link where you can study dome geometry.
A link from Samir Patel on domes in low cost housing